The present invention relates to a rotary viscous vibration damper or a rotary viscous vibration absorber.
Rotary viscous vibration dampers or rotary viscous vibration absorbers are known per se. Dampers or absorbers of this type are used to reduce rotary vibrations on crankshafts of reciprocating piston engines. Vibration damper rings or vibration damper masses are mounted within the housing of dampers or absorbers of this type. Here, the housing usually has a hub part which can be fastened to a crankshaft of an engine, in particular of an internal combustion engine. It is possible for the vibration damper ring to be rotated relative to the hub part. A shear gap, which is filled with a liquid shearing medium such as the abovementioned silicone oil, is formed between the hub part and the vibration damper ring. Flange bushings serve to guide and mount the vibration damper ring in the shear gap which is filled with silicone oil.
The flange bushings are usually inserted without prestress between the two damper housings and the vibration damper ring in order to allow the housing and the ring to slide on the flange bushings with as little friction as possible.
It is problematic at high temperatures, in particular at temperatures above 130° C. which regularly arise in rotary vibration dampers during driving operation on account of the shearing of the damping medium of silicone oil, that interactions frequently occur between the conventional flange bushings (which are, as a rule, manufactured from polyamide) and the silicone oil. These interactions lead to very rapidly progressing degeneration of the viscosity of the silicone oil. For instance, a decrease in the viscosity by 53% after a period of approximately 20 hours has been determined in tests at a rotary viscous vibration damper external temperature of 160° C. The service life of rotary viscous vibration dampers of this type is, as a rule, 20,000 hours. Here, wear of only 30% is aimed for in this time period.
In order to solve this problem, an attempt might first be made to reduce the high operating temperature, which does not appear probable, however, on account of installation space restrictions and relatively high peak pressures of the engines, with the result that the rotary viscous vibration dampers tend to have to be designed for withstanding even higher temperatures. Therefore, it also does not appear appropriate to design the rotary viscous vibration dampers in such a way that they are not subjected to high temperatures of this type during operation.
It is therefore an object of the present invention to provide a rotary viscous vibration damper or a rotary viscous vibration absorber which, even at temperatures above 130° C., ensures a longer service life than conventional rotary viscous vibration dampers or absorbers.
This and other objects are achieved according to the invention by a rotary viscous vibration damper or a rotary viscous vibration absorber having a hub part which can be fastened to a crankshaft of an engine, in particular of an internal combustion engine, and a vibration damper ring which is mounted such that it can be rotated relative to the hub part. A shear gap, which is filled with a silicone oil, is configured between the hub part and the vibration damper ring, in which shear gap flange bushings for guiding the vibration damper ring are mounted. The flange bushings are made of a liquid crystal polymer.
The rotary viscous vibration damper or absorber according to the invention is distinguished by the fact that the flange bushings consist of a liquid crystal polymer (LCP). It has been shown that this material does not interact, or interacts merely to a negligible extent, with the silicone oil even at relatively high temperatures, in particular above 130° C.
The use of flange bushings according to the invention of this type in a rotary viscous vibration damper or absorber makes a longer service life of the rotary viscous vibration damper or absorber possible in comparison with conventional rotary viscous vibration dampers or absorbers with flange bushings which consist, for example, of polyamide.
A further advantage of the rotary viscous vibration damper or absorber according to the invention consists in that, on account of the reduced heat sensitivity of the flange bushing material with regard to the interaction with the silicone oil, higher vibration damper temperatures can be permitted in comparison with the working temperatures of conventional rotary viscous vibration dampers or absorbers. As a result, a reduction in installation space and/or savings of material, in particular as a result of the omission of the fan disks or at least smaller dimensioning of the fan disks, is made possible. All of the abovementioned measures serve to reduce the vibration damper temperature, in order to reduce the degeneration of the viscosity of the silicone oil as a result of interaction with the material of the flange bushings.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.